Magnetic core



Sept. 17, 1946; A, U, WELCH, JR n 2,407,626

MAGNETIC CORE Filed Deo. 30, 1942 3 Sheets-Shet l H24. MT

Inventor: l Alansor LLM/eich J'f`,

by jaw/f. Mw

Sept. 17, 1946. A. u. wELH, JR 2,407,626

MAGNETIC com. I

Fi'led'nec. so, 1942 :s sheets-sheet 2 Y inventori Ansorw LLVVelcl Jfj Se'P-- -17, '1946. A. u. WELCH, JR 2,407,626

` MAGNETIC coR Filed 1m.l 30,71942 ssneets-sheet s lmvetor: Al'anson LLWeIchJ'r:

His Attorney.

Patented Sept. 17, 1946 MAGNETIC CORE Alanson U. Welch, Jr., Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application December 30, 1942, Serial No. 470,580

16 Claims. 1 My invention relates to laminated magnetic core structures for electrical induction apparatus such as transformers and reactors.

In the usual construction of magnetic cores,

the laminations are cut or punched from rela-- tively large stock sheets which are produced by rolling from bars or billets of a suitable magnetic material, such as various steel alloys, such as silicon steel or a magnetic nickel iron steel. It it known that the rolling process produces a grain structure in sheets which may extend in the direction in which the sheets have been rolled. It is further known that the path of least magnetic resistance of such material is generally in the direction that the sheets have been rolled, though in certain types of steels the most favorable magnetic direction, in so far as low flux losses are concerned, may be at sorne angle with respect to the direction of rolling. Thus, it will be seen that for optimum results for magnetic cores it is desirable to cut the laminations from the sheets of magnetic material so that the core iiux path is parallel with the path of least magnetic resistance, or parallel with the direction of rolling even at the corners.

One common form of magnetic core consists of a stack of L shaped punchings, but it will be apparent that such shapes cannot be punched as a single piece from a standard stock in such a manner that the most favorable magnetic direction extends parallel with the flux path in both parts of the punchings. This is due to the fact that the grain extends in the same direction throughout all parts of the stock while the two parts of the L shaped punchings are at right angles to each other. Another common form of a core consists of a rectangular core with adjacent laminations being stacked at right angles with respect to each other. While the most favorable magnetic direction in this type of core may be made parallel with the direction of the ilux path throughout the central portion of the laminations, the core iiux must cut crosswise of the most favorable direction at the ends of the laminations in traversing from one core leg to the next. Due to this crosswise flow of flux at the corners of the core, relatively high losses occur at these points.

One way oi' overcoming the difliculties referred to above is to provide a core structure by winding a ribbon of suitable magnetic steel so that al1 the nux will pass parallel to the direction of rolling of the material or in the direction which has the least magnetic reluctance. Such a type of wound core has been found to be very successful in the production of relatively small size transformers, which are called distribution transformers in the trade. Due to Various mechanical difficulties, however, it has been less economical to Wind much larger sizes of ribbon sheet material so as to produce sufficiently large cores for electric apparatus having a high kv.-a. capacity.

Another way of providing cores of laminated material in which the direction of flux path is along the line of least magnetic reluctance in the vicinity of the joints is to assemble the laminations, each corner of which has been cut on the diagonal, so as to provide a mitered joint at each of the corners. It will be seen, however, that when each of the joints at the various corners of the rectangular core are coincident with the diagonal running from the inside corner to the outside corner, all of the joints will be in substantial registry so that the possibility of gaps being formed at the joints for increasing the magnetic reluctance is appreciable, even though elaborate means are provided for clamping the magnetic laminations together.

An improved arrangement for providing mitered joints at the various corners of the assembled laminations and for preventing separation at the joints is described and claimed in patent application S. N. 376,304, Graniield, filed January 28, 1941, and assigned to the same assignee as this present invention. In that application there is described a stacked laminated core formed of laminations which have staggered mitered butt joints with extensions and corresponding indentations in the edges of the adjacent laminations, so as to prevent an appreciable gap from being formed at the butt joint. The various layers which are stacked to form the core are made up of similarly assembled laminations which are oppositely arranged so as to stagger the joint between laminations between one layer and a contiguous layer. In this manner there will be a minimum of magnetic iiux which will pass crosswise of the most favorable magnetic direction and due to the projections and corresponding intertting indentations which may extend in opposite directions for the adjacent joints of contiguous layers an overlapping will be provided at the joints so as to substantially preclude separation of the laminations of the assembled core.

There is also described in an application S. N. 470,578 to Brand, filed concurrently herewith, and assigned to the same assignee as this present invention, a corner construction which provides a minimum of magnetic reluctance at the corners and which also provides overlap so as to minimize separation of the stacks of the assembled core. In the construction of this copending application mitered butt joints are provided at the corners of each layer of laminations, the joints between laminations of one layer being displaced or onset :from the adjacent joint or a contiguous layer. The offsetting is obtained by cutting one edge of each of the laminations on a diagonal so that the joints will be coincident with the diagonal running from the inside to the outside corner of the assembled lamina# tions and cutting each of the other ends of the laminations with a mitered butt joint which is offset or displaced from a diagonal running from the inside corner to the outside corner of the assembled laminations. These latter joints are obtained by notching the corner or providing a first portion which is parallel with a longitudinal of the assembled core and a second portion of a corner which is parallel with the diagonal. The laminations are then stacked to provide layers and the layers are oppositely arranged so that the joints between laminations of one layer will be offset from joints between laminations of a contiguous layer. lIhus, a joint between laminations oi one layer which is coincident with the diagonal will be adjacent to but staggered from a joint of the adjacent or contiguous layer which is offset from the diagonal.

An object of my invention is therefore to provide an improved corner construction between laminations to form a core of the type described in the aboveementioned Brand application,

Another object of my invention is to provide a new and improved magnetic core stack of Ipunched laminations which has a minimum of electrical power loss throughout the magnetic circuit.

A further object of Imy invention is to provide a new and improved core. construction which is simple in construction, economical to manufacture, and eiiicient in operation.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawings, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification,

In the drawings Fig. 1 is an exploded perspective viewv of a laminated core comprising a plurality of layers of laminations formed according to an embodiment of my invention, Figs. 2 and 3 illustrate curves which will be employed in the description of my invention; Fig. 4 illustrates a method by which the laminations employed in the core of Fig. 1 may be cut from a single strip with loss; 5 is an` exploded perspective view f a three-legged core which is provided with an embodiment of my invention; Fig, 6 illustrates a method by which some of the laminations employed in the core of Fig. 5 may be cut from a single strip of magnetic material with a minimum of waste; Fig. '7 is an exploded perspective view illustratinga modification of the three phase core of Fig. 5, and Fig. 8 illustrates a method by which some of the laminations employed in the construction of Fig. '7 may be cut from a strip of magnetic material with a minimum of waste.

lin Fig. i of the drawings I have illustrated a magnetic core construction including a plurality of assembled laminations to form layers of laminations. The assembled core includes a layer It having leg sheets II and I2 and yoke sheets I3 and Iii, As has already been stated when laminations are punched with edges which are coincident with a diagonal running from an inside corner to an outside corner of the assembled lamination the joints will be in registry and thus there is a possibility of the adjacent laminations of each layer pulling apart to form gaps at the joints which will greatly increase the magnetic reluctance of this circuit, It is therefore desirable to stagger the joints and still provide a mtered butt joint which type of joint produces a minimum of magnetic reluctance at the joint or corner as it provides a minimum of distance in which the flux need pass crosswise of the most favorable magnetic direction.

One way of accomplishing this, as described and claimed in the above-mentioned Brand application, is to provide butt joints which are coincident with the diagonal and butt joints in which the major portion thereof is oiiset but still parallel to the diagonal running from the inside corner to the outside corner of the assembled lamination. With such a construction an overlapping will be provided when stacks of laminations are oppositely arranged and a relatively short distance will be provided at the corners at the overlapping in which the flux must pass crosswise oi the grain. I have found another arrangement of providing overlap and producing a minimum of magnetic path at the corners in which the flux must pass crosswise of the grain at the corners may be produced by so forming the laminations that each of the mitered butt joints at the corners will be offset from an adjaH cent diagonal running from the inside corner to the outside corner or" the assembled lamination. With this construction each of the offsets may be closer to the diagonal and still provide a suiiicient overlap than with the construction where all the overlap is provided by displacing the gap on one side only of the diagonal. Thus, in Fig. 1 I have illustrated a core construction including a layer Ill having laminations II, I2, I3 and I4, each of the laminations being provided With a broken line joint the major portion thereof being parallel with the diagonal running from the inside cor. er to the outside corner of the assembled laminaticns. Thus, one edge of the lamination I I has an edge surface I5 which is parallel with a lateral axis of the assembled core or perpendicular to the axis of the lamination, and a second edge portieri IB which is parallel with the adjacent diagonal running Jfrom the inside corner II to an outside corner I8 of the assembled lamlna tions In like manner the opposite end of the lamination i i has an edge portion I9 parallel with the lateral axis of the assembled lamination and a second portion 20 which is onset but parallel to the adjacent diagonal running from the inside corner to the outside corner of the assembled lammation. The adjacent end of the lamination I 3 is so constructed as to snugly fit the broken line joints, the lamination i3 having an end portion 2l which is parallel with the lateral axis of the assembled laminations or parallel tothe axis of the lamination IEB, and a second portion 22 which is parallel with a diagonal running from the inside corner to the outside corner. Thus, the portions of the joint which are parallel with the diagonal are offset from the diagonal by an amount Ii'oportional to the distance of the offset portions I9 and I5 or notch 2|. In order to provide a corner for the assembled laminations which is offset from the portion 28 of the lamination Il it will be seen that the edge portion of the lamination I3 has a short portion 23 which extends parallel with the longitudinal axis of the core before the corner is formed. It will be seen that the opposite end of the lamination I3 is similarly formed and therefore has a surface Iportion 24 to provide a joint which is parallel with the lateral axis of the assembled laminations, and a second portion 25 which is parallel and offset from the adjacent diagonal running from the inside corner to the outside corner of the assembled laminations. It will also be seen that the lamination I2 is a duplicate or equivalent to the lamination Il, While the lamination I4 is a duplicate of the lamination I3.

In order to provide a staggering of the joints between the layer l0 and an adjacent layer 30 the laminations which form the layer are formed of laminations 3l, 32, 33, and 34. Since,

in the construction as illustrated in Fig. l, the lamination 3l of layer 30 is placed at right angles to the lamination I3 of layer Il), the mitered butt joint between the laminations 3| and 33 is placed on the side of a diagonal opposite to the joint formed by the edges 20 and 22, by forming the ends of the lamination 3l similar to the ends of the lamination I3. Thus, the lamination 3l has an edge portion which is parallel with the longitudinal axis of the assembled lamination or parallel with the axis of the lamination 3|, and a second portion 36 which is parallel with the adjacent diagonal running from an inside corner 3'! to an outside corner 38 of the assembled laminations. In like manner the opposite end of the lamination 3l is formed with an edge portion 33 which is parallel with the longitudinal axis of the assembled laminations and a second portion 40 which is parallel but oiIset from the diagonal running from an inside corner 4 I to an outside corner 42 of the assembled laminations. With this construction it will be noted that the edge portions 20 and 22 will be on one side of the adjacent diagonal while the edge portion 40 will be on the opposite side of a diagonal. This is obtained since the offset portions I9 and 2I at adjacent corners of the contiguous laminations are parallel with the lateral axis of the assembled core, while the edge portion 39 is parallel with the longitudinal axis of the core. It will be seen that the lamination 33 has an edge portion 43 which is parallel with the longitudinal axis of the assembled laminations and a second portion 44 which is parallel with the diagonal. Furthermore, the opposite end of the lamination 33 has a portion 45 which is parallel with the longitudinal axis of the assembled laminations and a second portion 43 which is parallel with the diagonal. It will be apparent that the lamination 32 is an equivalent to the lamination 3l while the lamination 34 is an equivalentl to the lamination 33.

It will be seen in view of the above that when a layer IU is assmbled contiguously with a layer 30, the joints at corners of the contiguous laminations will be symmetrically disposed on opposite sides of the adjacent diagonal running from the inside corner to the outside corner. Thus an overlapping is provided with a minimum of fiux path being provided which is at an angle 0r crosswise to the line of lowest magnetic resistance.

I have illustrated in Fig. 2 a comparison between the magnetic characteristics of my imconstruction having rectangular corners which are overlapped. Thus, in Fig. 2 I have plotted on the abscissa axis per cent loss and on the ordinate axis per cent flux density. Curve 50 represents the loss in the corners of the conventional core made with rectangular sheets stacked with overlapping corners while curve 5I represents the characteristics of my improved corner construction. In Fig. 3 I have illustrated the exciting current in which per cent exciting current is plotted as abscissa and per cent ux den sity on the ordinate axis. Curve 52 represents the characteristics of an entire conventional core having rectangular overlapping corners while curve 54 represents the characteristics of the entire core formed with my improved joint construction.

My improved corner construction not only produces a core which is very efficient magnetically but it also produces a core which may be eniciently manufactured by punching out the various laminations from a single sheet of magnetic material having the proper flux orientation. Thus, in Fig. 4 I have illustrated a strip of magnetic material 60 from which all the laminations may be formed by punchings simultaneously with two different dies and I have marked the punchings to show that the laminations fit together so that they may be punched from the ribbon 6i) with no waste.

In view of the above it will be seen that I have provided an assembled core formed of various assembled layers which have a minimum of magnetic reluctance at the corners Furthermore, the various laminations may be formed from strip material having a single width and may be punched with only two different dies or with one die if the steel is reversed for making alternate cuts. Furthermore, the ends of all similar punchings are similar and the laminations may be cut without waste.

It is to be understood that my invention has application for a core having any suitable number of punchings in each layer, and in Fig. 5 I have illustrated a core having three legs which has particular application to a three phase electrical apparatus. The illustrated construction includes a layer 53 including three leg sheets and four yoke Asheets which are so punched that the adjacent butt joints between laminations of contiguous ilayers may be displaced on opposite sides of a diagonal running from an inside corner to an out- 'side corner of the assembled laminations or some Ajoints are displaced on the leg side and some on the yoke side of the adjacent diagonal between inner and outer ends of the corner. Thus the layer 60 includes a leg sheet 6I, o-ne end having an edge surface or notch 62 Iwhich is parallel with a lateral axis of the assembled laminations and a second edge portion 63 which is parallel but oiiset from an adjacent diagonal running from an inside corner 64 to an outside corner 65 of the assembled laminations. A cooperating yoke sheet 66 has a straight or extending portion 5l which cooperates with the portion 62 of the leg sheet and a second portion 68 which cooperates with the edge portion 63 of the leg sheet 6I. Similarly, a yoke sheet 69 is provided which is an equivalent to the yoke sheet 66 and includes a portion lil which cooperates with a notched portion 'Il of the leg sheet 6l, both of which are parallel with the lateral axis 0f the assembled laminations. The remainder of the substantially mitered butt joint is provided by a surface 'I2 of the lamination 619 and a surface 'I3 of the leg sheet SI, both of which are parallel and offset from a diagonal running between the corners of the assembled laminations. The oisetting of the joints at the ends of the other cuter leg sheet 91 is provided by providing the extensions in the leg sheet 91 instead of in the yoke sheet, as is done on the opposite side. Thus7 the leg sheet 91 is provided with an extension l!! or a portion parallel with the longitudinal axis of the assembled lamination, and a second portion which is parallel and offset from the adjacent diagonal. Cooperating with these corner surfaces there is provided a yoke sheet having a portion 'l1 which is parallel with the longitudinal axis of the assembled laminations and a second portion "i3 which mates with the edge portion of the leg sheet 91. Similarly a yoke sheet 19 is provided which has a similar conguration as the yoke sheet 16 and includes an edge portion tti which mates with an edge portion 8| or the leg sheet 91. The yoke sheet 19 is also provided with an edge portion i2 which cooperates with an edge portion 33 of the leg sheet, these latter portions being parallel and oil'- set from the adjacent diagonal. The opposite end of the yoke sheet 19 is provided with an edge mating surface portion t4 which is also parallel with the longitudinal axis and a second portion 85 which runs diagonally at a suitable angle such as 45 degrees from the edge portion 84. In like manner a similar end of the yoke sheet 16 is provided with an edge portion 85 which is parallel with the longitudinal axis of the assembled lamination and a second portion 81 which runs diagonally at a suitable angle or l5 degrees from the edge portion t5. Cooperating with the edges of the yoke sheets there is provided edges of a center leg sheet 88 and edges of the yoke sheets 5E and rlhus the leg sheet S8 is provided with an edge portion t9 which mates with the portion Sill of the yoke sheet 19 and a second portion y9|) which mates with a part of the diagonally extending edge 35. The remainder of the edge 85 cooperates with an edge 9| of the yoke sheet 59. Another angular edge portion il?. oi' the yoke sheet G9 cooperates with a similar angularly extending edge portion S3 of the leg sheet 8S. The angularly extending edge 93 is offset by providing another edge portion 94 of the leg 58 which is parallel with the lateral axis of the assembled lamination. A similar edge portion is provided on the yoke sheet 59 which mates with the edge portion Bil. A similar joint is provided at the other end oi the leg sheet between the yoke sheets 55 and 15. It will therefore be seen that when stacking a layer of laminations 95 which is composed of laminations similar to that forming a layer |59 but laterally reversed, the adjacent joints between contiguous laminations will be on opposite sides of the adjacent diagonal running between corresponding inside and outside corners of the assembled laminations.

In the construction illustrated. in Fig. 5 it will be seen that the joints at either endv or the leg sheet 6| are on the leg sheet side of the diagonal while the joints on either end of the leg sheet 91 are on the yoke side of the diagonal of the assembled laminations. However, it is to be understood that the joints of the laminations may all be staggered on one side or they may be staggered' on either of the sides of the diagonals between the corners of the assembled laminations as is convenient.

In Fig. 6 I have illustrated how all the laminations with the exception of the center leg sheet 88 may be punched from a single ribbon of steel with a minimum or waste. It will beA seen that the only Iwaste is a small triangular piece which must be removed from the ends of the yoke sheets `Bti and 59 so that they will have the suitable `v' shape to cooperate with the ends of the center leg and adjacent yoke sheets. The center leg 88 may be formed by cutting a triangularly shaped piece from sheets having the shape of the leg sheets 6I and B1.

In Fig. '1 I have illustrated a modification of a three legged core design which may be either employed as a three phase core 0r since the center leg is about double the width of the two outer legs it may be advantageously used as a three legged single phase core. The construction includes a layer of laminations IUE) having three leg sheets and four yoke sheets, the staggering of joints being provided by an adjacent layer IBI composed of laminations similar to those that make up layer |00 except being laterally.

reversed. The layer IBG includes a leg sheet |02 having an edge or notch |03 which is parallel with a lateral axis of the assembled laminations and a second portion IM which is parallel to but offset :from a diagonal running between the adjacent corners of the assembled lamination. The adjacent yoke sheet |05 has an edge or extending portion |06 which cooperates with the notch |53 and a second portion |01 which cooperates with the diagonal portion ||J4 of the leg sheet |52. The opposite end of the leg sheet ltd is similarly formed with an edge portion 0r notch |33 which is parallel with the lateral axis of the assembled laminations and a second portion IUS which runs diagonally from the portion |08 and parallel and offset from the diagonal running between the corners of the assembled laminations. In like manner a yoke sheet IID is provided with a portion III which mates the portion Hi8 and a diagonal portion I|2 which cooperates with the portion |59. The other outer leg sheet i3 is provided with an extending p0rtion II4 which is parallel with the longitudinal axis of the assembled laminations and a second portion I I5 which runs diagonally and oiset from the diagonal running between the corners. Similarly a yoke sheet IIS is provided with an edge portion or notch I|1 which cooperates with the edge portion |I4 and a second portion IIB which cooperates with the portion |I5. The opposite end of the leg sheet I|3 is also provided with a joining surface including portions I|9 and |20 and an adjacent yoke sheet I2| has a notched portion |22 which cooperates with the edge IIS and a portion |23 which cooperates with the edge portion |25. A center leg |24 is provided having an extending portion |25 which cooperates with a similarly shaped notch portion |26 of the yoke sheet I2| which runs parallel with the longitudinal axis of the assembled laminations and a diagonally extending portion |21 which cooperates with the portion |28 of the yoke sheet I2I. The same end of the center leg |24 is provided with a diagonal cut portion |39 and a notch portion |3| which is parallel with the lateral axis of the assembled laminations. Cooperating with these two surfaces is a diagonally running portion |32 of the adjacent yoke sheet Ill and a portion |33 which runs parallel with the lateral axis of the assembled laminations. So that the yoke sheet IIU may be cut from a ribbon sheet without a minimum waste a corner may be cut o as is shown at |34. The upper end of the leg sheet |24 and the cooperate ing ends of the yoke sheets |65 and IIi are similarly formed.

Since all the laminations except the center leg ysheet |24 are of similar width they may all be punched from asimilar ribbon of steel and in Fig. 8 I have illustrated how all the laminations except the center leg 24 may be cut from a single ribbon of steel with no waste and I have illustrated by similar numerals how the various ends of the laminations t together with no waste.

Although I have shown and described particular embodiments of my invention, I do not desire to be limited to the particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A magnetic core comprising a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, said layers including at least four assembled laminations with diagonal butt joints at adjacent ends, said layers having at least two dissimilar symmetrical laminations with each of said laminations having edge surfaces in six planes, edge surfaces in four of said planes forming the edges for said butt joints of said laminations.

2. A magnetic core comprising a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations of each layer ,having substantially mitered butt joints between ends so that a minimum of lux passing from one lamination to another will pass crosswise of the most favorable magnetic direction, said core structure comprising three leg members and yoke members connecting the ends of said leg members forming a substantially rectangular core having two substantially rectangular windows, said mitered butt joints at the corners between said outer leg and yoke members of said core structure being oiset from an adjacent diagonal running from the inside corners to the outside corners of the assembled laminations, said adjacent joints between adjacent laminations of contiguous layers being oiTset on opposite sides of said adjacent diagonal so as to provide overlapping between adjacent laminations of contiguous layers at said joints.

3. A magnetic core comprising a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations of each layer having substantially mitered butt joints between ends so that a minimum of flux passing from one lamination to another will pass crosswise of the most favorable magnetic direction, said core structure comprising three leg members yoke members connecting the ends of said leg members forming a substantially rectangular core having two substantially rectangular windows, said mitered butt joints at the corners between said outer leg and yoke members of said core structure being oiset from an adjacent diagonal running irom the inside corners to the outside corners of the assembled laminations, some of said joints being oiset on the leg side of said adjacent diagonal and some of said joints being offset on the yoke side of said diagonal.

4. A laminated magnetic core having at least four punchings of magnetic strip material per layer, the two ends of each punching consisting of a major portion at azi angle of forty-five degrees with the lengthwise dimension oi the punching and a minor portion perpendicular to the lengthwise dimension of the punching, the two perpendicular minor portions at the opposite ends of each punching being adjacent the same side of the punching.

5. A laminated magnetic core having at least iour punchings of magnetic strip material per layer, the two ends of each punching consisting of a major bias cut portion and a minor portion out perpendicular to the lengthwise dimension of the punching, the two perpendicular minor portions at the opposite ends ol each punching being adjacent the same side of the punching.

6. A punching for a mitered joint magnetic core, said punching having straight sides parallel with its lengthwise dimension and broken line ends, each broken line end comprising a minor portion perpendicular to the lengthwise dimension of the punching and a major portion making an angle of forty-ve degrees with the lengthwise dimension of the punching, said perpendicular minor portions extending for equal distances from the same side of said punching, said forty-five degree major portions being perpendicular to each other.

'7. A punching for a mitered joint magnetic core, said punching having straight sides parallel with its lengthwise dimension and broken line ends. each broken line end including a minor portion perpendicular to the lengthwise dimension of the punching, said perpendicular minor portions extending for equal distances from the same side of said punching.

8. A stacked lamination core having generally mitered butt joints in each layer which joints are staggered in adjacent layers, each layer comprising a plurality of punchings having straight sides parallel with their lengthwise dimension and having broken line ends, each broken line end comprising a minor portion perpendicular to the lengthwise dimension of the punching, said perpendicular minor portions extending for equal distances from the same side of said punching.

9. A stacked rectangular magnetic core composed of two different kinds of leg punchings and two different kinds of yoke punchings, said punchings all being o-f equal width with ends which are generally bias cut, odd-numbered lamination layers of said core each comprising two leg punchings of the same kind and two yoke punchings of the said kind, even-numbered lamination layers each comprising two of the other kind of leg punchings and two of the other kind of yoke punchings.

l0. A stacked rectangular magnetic core composed of two diiierent kinds of leg punchings and two different kinds of yoke punchings, said punchings all being of equal width with ends which are generally bias cut, odd-numbered lamination layers of said core each comprising two leg punchings of the same kind and two yoke punchings of the same kind, even-numbered lamination layers each comprising two of the other kind of leg punchings and two of the other kind of yoke punchings, one kind of leg punching being identical except for length with one kind of yoke punching and the other kind of leg punching being identical except for length with the other kind of yoke punching.

1l. A stacked rectangular magnetic core composed of two diierent kinds of leg punchings and two diierent kinds of yoke punchings, said punchings all being of equal width with ends which are generally bias out, odd-numbered lamination layers of said core each comprising two leg punchings of the same kind and two yoke punchings of the same kind, eveiinumbered lamination layers each comprising two of the other kind of leg punchings and two of the other kind of yoke punchings, one kind of leg punching being identical except for length with one kind of yoke punching and the other kind of leg punching being identical except for length with the other kind of yoke punching, the leg and yoke punchings in each layer being different in shape as well as in length.

12. A laminated overlapping mitered joint magnetic core having at least four magnetic punchings per lamination layer, each of the magnetic punchings being symmetrical about an imaginary bisector perpendicular to the length of the punching.

13. A three-legged magnetic core consisting of stacked lamination layers, each layer comprising seven I type punchings of which three are leg punchings and four are yoke punchings, all of said punchings having generally bias cut ends which are interiitted to form generally mitered butt joints in each layer, all of said yoke punchings and at least the two outside leg punchings being of equal Width.

14. A three-legged magnetic core consisting of stacked lamination layers, each layer comprising seven I type punchings of which three are leg punchings and four are yoke punchings, all of said punchings having generally bias cut ends which are intertted to form generally mitered butt joints in each layer, all of said yoke punchings and at least the two outside leg punchings being of equal width, the center leg punching being substantially twice as Wide as the othei` punchings.

15. A single phase shell type laminated core having a central winding leg and oppositely eX- tending yoke portions which are substantially narrower than the winding leg, said core being made of straight magnetic pieces in each lamination layer, each piece having a most favorable magnetic direction coinciding with its length, the ends of said pieces being generally bias cut to form mitered butt joints therebetween, said mitered joints being offset from each other in successive layers so as to form overlapping mitered core joints.

16. A single phase shell type laminated core having a central leg portion of twice the area oi its two oppositely extending yoke portions, said core being made of an equal number oi straight magnetic pieces in each lamination layer, each piece having a most favorable magnetic direction coinciding with its length, the ends of said pieces being generally bias cut to form mitered butt joints therebetween, said mitered joints being oilset from each other in successive layers so as to form overlapping mitered core joints in which the core flux will be substantially parallel with the most favorable magnetic direction of the pieces.

ALANSON U. WELCH, JR. 

